Cam-operated guiding device and moulding installation using same

ABSTRACT

A cam-operated guiding device for controlling a related movement of a member which is moreover continuously displaced, the device including two mutually transversely offset parallel cams with which co-operate respectively two coaxial rollers for bilaterally guiding said member. One of the cams is mounted via elastically deformable members designed to allow an elastic displacement of the cam relative to the other cam.

[0001] The present invention relates to improvements to cam-type guidingdevices for controlling a related movement of a member that isindependently driven with a continuous displacement, said devicecomprising two parallel cams, offset transversely from each other,acting on two respective coaxial rollers for bilateral guidance of theabovementioned member.

[0002] To express things more concretely, a device of the kindconsidered here is illustrated in FIGS. 1 and 2 of the appendeddrawings, which are, respectively, a top view of the guiding device anda partial view of the same device shown in cross section taken on theline marked II-II in FIG. 1. Fixed on a common base 1 are two elongateparts 2 and 3, usually made of steel, whose opposing edges 4 and 5,respectively, have a curved longitudinal profile while also beingparallel with each other. These cam edges are designed to guidepositively, by bilateral contact, a roller. Since, however, the singleroller cannot be in simultaneous contact with both cam edges 4 and 5,the two cams 4 and 5 are offset transversely with respect to each otherand two rollers 6 and 7 are mounted on the same spindle 8 in contactwith the respective cams 4 and 5, the spindle 8 being carried by themember 9 which is to be guided or by an accessory of the member that isto be guided.

[0003] Such guiding devices find application particularly, though notexclusively, in moveable, and in particular rotating moldinginstallations with jackknife molds for the production, by blow moldingor stretch-blow molding, of containers, such as bottles, inthermoplastic polyester, such as PET, from a heated preform, saidinstallations comprising a cam and roller-type guiding device forcontrolling the opening and closing of said jackknife molds, at the sametime as said molds are driven with a continuous displacement.

[0004] In installations of the kind indicated, usually laid out in theform of a rotating carousel carrying several, sometimes several tens ofjackknife molds, the cam and roller-type guiding devices used to openand close the molds have been perfectly satisfactory as long as the rateof production of the containers (and therefore the speed at which theinstallation is run) remains below a certain threshold.

[0005] However, problems have occurred when speeding up the installationto increase the rate of production of containers in response to userdemand: the installation has become noisy and malfunctions havedeveloped, not only mechanical but also electrical or electronic, and itproved impossible to find the source of these.

[0006] Lastly, measurements carried out on the instantaneous loadsbetween cams and rollers have revealed that the actual loads areconsiderably higher (some ten times higher) than those estimated.

[0007] It was then discovered that, at the higher speeds at which it waswished to run the installation, the rollers did not stay in continuouscontact with the cams, and that this contact was accompanied by aphenomenon of rebound caused by the rollers coming too suddenly intocontact with the cams. The two opposing cams are of course fixed rigidlyto a common base and define between them a passage that offers only avery small amount of play for the two coaxial and contra-rotatingrollers of each pair of rollers.

[0008] It is therefore the conjunction of this rebound phenomenonoccurring to a significant extent, with the insufficient amount of playbetween the cams which gives rise to vibrations that propagate throughthe installation and give rise to the noises and malfunctions observed.

[0009] In addition to this, several successive molds are operatedsimultaneously while at different functional phases. The cams aretherefore very long and several pairs of rollers are engagedsimultaneously in contact with them. The successive rebounding ofconsecutive pairs of rollers naturally generates resonance which furtheraggravates the problems discussed above.

[0010] It is a basic aim of the invention to find a solution to theproblems observed hitherto and to provide an improved arrangementdesigned to lead to a stable and regular operation which will no longergenerate vibrations and which, in addition, will enable the speed ofoperation of the installation to be further increased.

[0011] For these purposes, a guiding device as set out in the preambleis characterized, being constructed in accordance with the invention, inthat one of the cams is mounted via elastically deformable means,capable of allowing an elastic displacement of said cam relative to theother cam.

[0012] By means of this arrangement, the elastically mounted cam is ableto absorb the shock when the roller strikes it and the reboundphenomenon is if not eliminated at any rate greatly attenuated andrapidly damped. The vibrations are eliminated or at any rate greatlyattenuated in the installation, which as a result becomes less noisy.

[0013] In a preferred embodiment, the elastically deformable meanscomprise a block of elastically deformable, and in particular anelastomeric material interposed between said cam and a supporting baseon which the other cam is mounted in a fixed manner. However, othertechnical solutions are of course conceivable: for example, the camcould be fixed to a supporting base by threaded members with respectiveelastically deformable intermediate bushings between said threadedmembers and respective bores in the base.

[0014] To avoid the phenomenon of resonance due to the simultaneousengagement of several pairs of rollers with the two cams, it isadvantageous for said elastically mounted cam to be constructed in theform of several cam lengths arranged end to end, the number of theselengths being equal to or greater than the number of rollers capable ofbeing engaged simultaneously in contact with said cam and the length ofthe cam lengths being decided, in relation to the interval separatingsuccessive rollers, in such a way that each elastically mounted camlength is in contact with only one roller. Each cam length is thusmechanically disconnected from the adjacent length or lengths and ispushed back elastically only by the one roller with which it is incontact, no interference occurring with rollers situated upstream ordownstream.

[0015] To ensure that a step does not develop between the adjacent endsof two successive cam lengths causing a shock and therefore a vibrationresulting in a noise when a roller passes over it, it is envisaged thatthe continuity of the surface with which the roller is in contact beensured by the fact that two adjacent cam lengths meet with a mutualdiagonal overlap.

[0016] As indicated earlier, the arrangements of the invention find apreferred, but non-restrictive application to a moveable and inparticular rotating installation for the molding of containers, such asbottles, in thermoplastic polymer such as PET, for opening and closingthe jackknife molds.

[0017] A clearer understanding of the invention will be gained fromreading the detailed description of certain preferred embodiments givenpurely as non-restrictive examples. This description refers to theappended drawings, in which:

[0018]FIGS. 3 and 4 are partial schematic views similar to FIG. 2 andeach illustrate a different embodiment in accordance with the invention;

[0019]FIG. 5 is a top view, similar to FIG. 1, illustrating anotherpreferred embodiment of the provisions of the invention; and

[0020]FIG. 6 is a side view taken on the line marked VI-VI in FIG. 5, ofpart of the device of FIG. 5.

[0021] Referring first of all to FIG. 3, which is similar to FIG. 2except for the provisions of the invention, and in which the samereference numbers are repeated to denote identical parts, the twoelongate parts 2 and 3 are mechanically decoupled by mounting one of theparts (part 2 in the example illustrated) on the base 1 via elasticallydeformable means that allow an elastic displacement of the correspondingcam surface 4 relative to the other cam surface 5.

[0022] A variety of ways may be implemented to realize this provision.

[0023] In the preferred embodiment more particularly shown in FIG. 3,the elastically deformable means take the form of a block 10 of elasticmaterial, such as an elastomer, interposed between said elongate part 2and the base 1 on which the other elongate part 3 is still mounted in afixed manner.

[0024]FIG. 4 illustrates another possible embodiment in which theelongate part 2 is fixed to the base 1 by screws 11 with an intermediateelastically deformable bushing 12, of for example elastomer, between theshank of the screw 11 and the bore 13 cut into the part 2.

[0025] Whichever solution is adopted, the elongate part 2 can retreatlaterally, in other words the cam surface 4 can move transversely awayfrom the opposing cam surface 5 when the roller 6 applies an excessiveload to it, for example due to a rebound.

[0026] However, the proposed solution alone may prove insufficient whereseveral successive rollers are simultaneously engaged in contact withthe cam surface 4, because the reactions of the various rollers maycombine together and cause resonance.

[0027] In this case, it is highly advantageous to decouple the areas ofcontact between the cam 4 and the various successive rollers. In otherwords, the elongate part 2 is cut up into a number of cam lengths 2 ₁, 2₂, . . . , 2 _(n) equal to or greater than the number n of rollers 6 ₁,6 ₂, . . . , 6 _(n) that can be simultaneously in contact with said camsurface 4 all the way along its length. FIG. 5 illustrates oneembodiment laid out in this way: the cam surface 4 can be contactedsimultaneously by five rollers 6 ₁ to 6 ₅ and the elongate part 2 ismade up of five cam lengths 2 ₁ to 2 ₅ arranged one after the other.Because of the elastic mounting of each length 2 ₁ to 2 ₅ on the base 1,any shock or vibration communicated to one of the cam lengths is notretransmitted to the adjacent length(s).

[0028] As a matter of preference, it is desirable that the number oflengths should be at least one greater than the number of rollerspressing against the cam surface, in order to ensure that each lengthreceives the contact of only one roller.

[0029] In the configuration described above, the elastic mounting of thecam lengths 2 ₁ to 2 ₅ seems to be required to be done in the mostappropriate way by using an elastic block (or individual elastic blocks)as illustrated in FIG. 3 or elastic bushings as illustrated in FIG. 4.

[0030] In addition, to prevent shocks as a roller 6 passes from one endof one cam length 2 _(i) to the adjacent end of the next length 2_(i+1), particularly when one of them is offset transversely withrespect to the other, it will be preferable to use the arrangement shownin FIG. 6: the two adjacent ends of the successive lengths 2 _(i), 2_(i+1) meet not with butted cross sections but with complementarybeveled sections laid together to form a joint plane 14 which slopes inthe longitudinal direction of the cam, so that the passage of a roller 6from one length 2 _(i) to the other 2 _(i+1) is progressive.

1. A cam-type guiding device for controlling a related movement of amember (9) that is independently driven with a continuous displacement,said device comprising two parallel cams (4, 5), offset transverselyfrom each other, acting on two respective coaxial rollers (6, 7) forbilateral guidance of the abovementioned member, characterized in thatone of the cams (4) is mounted via elastically deformable means (10, 12)capable of allowing an elastic displacement of said cam (4) relative tothe other cam (5).
 2. The device as claimed in claim 1, characterized inthat the elastically deformable means comprise a block (10) of elasticmaterial interposed between said cam (4) and a supporting base (1) onwhich the other cam (5) is mounted in a fixed manner.
 3. The device asclaimed in claim 2, characterized in that the elastically deformablemeans comprise a block (10) made of elastomer.
 4. The device as claimedin claim 2, characterized in that the cam (4) is fixed to a supportingbase (1) by threaded members (11) with respective elastically deformableintermediate bushings (12) between said threaded members (11) andrespective bores (13) in the base (1).
 5. The device as claimed in anyone of claims 1 to 4, characterized in that said elastically mounted cam(4) is constructed in the form of several cam lengths arranged end toend, the number of these lengths being equal to or greater than thenumber of rollers (6) capable of being engaged simultaneously in contactwith said cam and the length of the cam lengths being decided, inrelation to the interval separating successive rollers, in such a waythat each elastically mounted cam length is in contact with only oneroller (6).
 6. The device as claimed in claim 5, characterized in thatthe number of lengths is at least one greater than the number of rollersengaged simultaneously in contact with the cam, by means of which eachlength receives contact from only one roller.
 7. The device as claimedin claim 5 or 6, characterized in that two adjacent cam lengths meetwith a mutual diagonal overlap.
 8. A moveable, and in particularrotating molding installation with jackknife molds for the production,by blow molding or stretch-blow molding, of containers, such as bottles,in thermoplastic polyester, such as PET, from a heated preform, saidinstallation comprising a cam and roller-type guiding device forcontrolling the opening and closing of said jackknife molds,characterized in that the guiding device is constructed in accordancewith any one of claims 1 to 7.